The present invention relates to photoelectric detectors and more particularly to photoelectric control units which periodically transmit light pulses and synchronously detect return pulses.
In the past photoelectric control units have been manufactured in a range of models each of which is suitable for a particular type of application environment. Furthermore, photoelectric control units have not been designed to provide the operator with much in the way of useful information about the unit's current settings or the conditions under which it is operating. Consequently, photoelectric control units have not had much flexibility for being used in different types of applications and have not been able to provide much information of the type the operator might, for example, use to align the unit. While some photoelectric control units have been designed to operate under microprocessor control these units have nevertheless not been designed to be especially user friendly or to offer the operator a wide range of operational settings suitable for different applications. Furthermore, most photoelectric control units have been susceptible to giving false signals due to electrical and optical noise occurring at the same frequency as the pulse repetition rate of the control unit itself. Such noise may be due to other photoelectric control units in the vicinity or simply due to other machinery having comparable operating frequencies. Nevertheless, when the noise is on frequency with the pulse repetition rate, ordinary pulse counting and synchronous detection techniques are not able to eliminate the noise problem. Additionally, most traditional photoelectric control units have not provided accurate measures of operating margin or reliable indications of overall operational stability. Operating margin has ordinarily been difficult to determine on account of the narrow voltage ranges over which most photoelectric control units operate and the difficulties with amplifier saturation which occur when such voltage ranges are exceeded. Satisfactory systems have not been developed for allowing a photoelectric control unit to determine its own operating margin in an accurate fashion over a broad range. Furthermore, even given measures of operating margin, the operational stability of a photoelectric control unit has been difficult to determine. Photoelectric control units can be affected by high noise levels in their operating environment which can degrade operational stability despite satisfactory levels of operating margin.
It is therefore an object of the present invention to provide a photoelectric control unit having a user friendly operator interface which allows for operator control over a wide range of operational settings in a convenient and understandable fashion so that the unit can be adapted for use in a large number of different applications.
It is another object of the present invention to provide a photoelectric control unit having a target acquisition system which is immune to electrical and optical noise occurring on frequency with the repetition rate of the photoelectric control unit itself.
It is a further object of the present invention to provide a photoelectric control unit which is capable of accurately measuring its own operating margin over a broad range of signal levels and providing a reliable indication of its operational stability as a function of operating margin and noise.
It is yet another object of the present invention to provide a photoelectric control unit in which the pulse repetition rate and operating range of the unit may be selected by the operator at the operating site through the use of a user friendly interface.
It is yet a further object of the present invention to provide a photoelectric control unit which is flexible in operation, provides useful information feedback to its operator, is otherwise reliable in operation and can be produced at a reasonable cost.